The invention relates to a swivel actuator device for lift control of a gas exchange valve in a cylinder head of an internal combustion engine.
Currently unpublished German Patent Application 101 40 461 describes a rotary actuator device for lift control of a gas exchange valve in a cylinder head of an internal combustion engine. The lift is controlled via an electric motor driven by engine characteristics maps; the rotor of this motor has a shaft with a control cam in a rotationally fixed connection. During operation of the internal combustion engine, the motor swivels and/or swings back and forth and the control cam periodically presses the gas exchange valve into its open position via a swivel lever. The gas exchange valve is closed by the spring force of a valve spring. An additional spring is mounted on the shaft in order for the electric motor not to have to overcome the total spring force of the valve spring in opening the gas exchange valve. The forces of the valve spring and the additional spring are such that in periodic operation of the rotary actuator device, the kinetic energy is stored either in the valve spring or in the additional spring, depending on the position of the gas exchange valve. As a result of this measure, the power consumption in operation of the rotary actuator device is reduced. The control cam is alternately controlled by the electric motor and has a single cam flank designed with a ramp serving for opening and closing between a cam cup and a base circuit; in a diametric area, the control cam has a base circle section that is lengthened in the circumferential direction for this cam flank, a stop face for a first rotational stop on the motor side or on the cylinder head side following this base circle section and being directed essentially radially to the cam cup region.
One disadvantage of the rotary actuator device described here is the high power consumption at low rotational speeds.
The object of the present invention is to reduce power consumption at low rotational speeds for a generic rotary actuator device.
This object is achieved by providing a second operating element having a first control path, situated on the first operating element. This invention expands the existing swivel actuator device through a second contrarotating operating element with a smaller lift in comparison with the main cam. This second operating element does not open the valve completely and is used only for small lifts in the range of low engine rotational speeds. At low rotational speeds of the internal combustion engine, the swivel actuator device receives electric current so that the shaft swivels only in the direction of the second operating element, whereas at high rotational speeds it is swiveled only in the direction of the first operating element. Due to the smaller lift, the swivel actuator device advantageously consumes less current at low rotational speeds.
In further embodiments, the two operating elements form a double cam which can be operated smoothly in two directions. In addition, it is simple and inexpensive to manufacture a double control path designed in this way, such that its zero lift ranges are next to one another.
With embodiments providing less than full lift, the power consumption is low at low rotational speeds. Furthermore, valve noise generated by the gas exchange valve striking the valve seat is reduced by the inventive design. The second operating element equalizes the torques of the spring element, an actuator spring, against the torques of the valve spring. The resulting torque on the camshaft is almost zero, depending on tolerances, and thus the camshaft can be kept almost currentless in any angular position of the second operating element. Such a system has low dynamics because it is built up merely by the torque buildup by the slewing motor (through electric power supply). Another advantage that can be mentioned is the improvement in the gas dynamics in load exchange because supersonic speeds can be generated in the valve gap due to the small valve lift, which thus makes a significant positive contribution toward good processing of the fuel mixture. In one embodiment in particular, system overshooting does not have any effect because the valve lift cannot be altered in these ranges.
To improve the low dynamics of the second operating element, the second control path may be divided into acceleration and deceleration. To do so, the control path is divided into two ranges. In the first lift range, above zero lift or a defined value (from 0.6 mm to 1.5 mm lift), the kinematic torque of the spring element is compensated only to a slight extent so that a spring-induced acceleration is impressed upon the swivel actuator device. In the second lift range (e.g., from 1.5 mm to approx. 3.5 mm), the kinematic torque of the spring element is overcompensated, so that a spring-induced deceleration is imposed upon the swivel actuator device over this lift range. Due to this design, it is possible in a simple way to have a positive influence on the dynamics of the swivel actuator device, especially at low valve lifts.
It is possible to arrange the two operating elements either radially on the outside circumference of the shaft, so that multiple gas exchange valves can be operated by one swivel actuator device, and/or apply a rocker arm path to the end face of the shaft so that a single gas exchange valve can be controlled with it.
The internal friction of the system is reduced with the arrangement of a power transmission element between the operating element and the gas exchange valve.
The inventive swivel actuator device according to patent Claim 12 may be arranged advantageously on the intake and/or exhaust ends of the cylinder head of the internal combustion engine. This principle of equal parts permits inexpensive production.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.